In recent years, glass panels having not only heat insulation performance but also heat shield performance have been developed. For example, there has been used a glass panel that is comprised of a colored heat-ray absorbing glass, a clear glass disposed in opposed relation to the heat-ray absorbing glass via spacers so as to form a hollow layer therebetween, and a low-emission transparent multilayer formed on an inner glass surface of the colored heat-ray absorbing glass, wherein the colored heat-ray absorbing glass is disposed on the outdoor side and the clear glass is disposed on the indoor side (see Japanese Patent Publication No. 2882728, for example).
As a low-emission transparent multilayer formed on a hollow-layer-side glass surface of a colored heat-ray absorbing glass disposed on the outdoor side, there has been disclosed a multilayer that provides a mechanism having solar radiation heat shield performance and high heat insulation performance (see Japanese Laid-Open Patent Publication (Kokai) Nos. S63-30212, S63-134232, and S63-239044, for example).
This low-emission transparent multilayer is constructed by stacking a total of (2n+1) layers including dielectric layers and metal layers on a glass surface and by forming a protective layer as the uppermost layer of the multilayer. It is known that as the dielectric layers, ZnO is excellent in film formation speed, and also, as the metal layers, Ag is excellent in heat-ray reflecting function.
Further, SiNx, TiO2, SiAlOxNy (sialon), or the like is known as the protective layer.
The above described low-emission transparent multilayer has the problem that the metal layers are corroded by migration thereof caused by the presence of moisture, oxygen, chlorine, and so on in the air. On the basis of this problem, the applicant of the present invention has previously obtained the knowledge that the above mentioned moisture and others present in the air pass through metal oxide layers (dielectric layers) formed on the metal layers to reach the metal layers. In order to prevent the corrosion to thereby improve the durability of the multilayer, the applicant has proposed to set the average crystal grain size of crystal grains constituting the metal oxide layers to 20 nm or less so as to make the metal oxide layers dense and prevent transmission of moisture through the metal oxide layers (see Japanese Laid-Open Patent Publication (Kokai) No. H09-71441, for example).
Further, the applicant of the present invention has previously proposed a low-emission transparent multilayer in which dielectric layers are separated from each other by an amorphous layer, and metal layers (Ag) have improved durability (see Japanese Laid-Open Patent Publication (Kokai) No. 2002-173343, for example).
However, in the case where the above-mentioned low-emission transparent multilayer is formed on a glass surface on a hollow layer side, the low-emission transparent multilayer is brought into a smoking or smoldering state by heat treatment carried out during manufacture of the concerned glass panel, and migration of the metal layer (Ag) in the low-emission transparent multilayer occurs to corrode the metal layer (Ag) and degrade heat shield performance.
The present invention has been developed in view of the above described problems. It is an object of the present invention to provide a heat insulating and shielding glass panel that is capable of maintaining heat shield performance even if the glass panel is subjected to heat treatment during manufacture.